Abstract : This paper explores the use of ultimate opening in urban analysis context. It demonstrates the efficiency of this approach for street level elevation images, derived from 3D point clouds acquired by terrestrial mobile mapping systems. An area-stability term is introduced in the residual definition, reducing the over-segmentation of the vegetation while preserving small significant regions. We compare two possible combinations of the Ultimate Opening and the Area Stability: first as a multiplicative factor, then as a subtractive term. On the one hand, multiplicative factor is very strict and many significant regions may be eliminated by the operator. On the other hand, a subtractive factor is more easily controlled according to the image dynamics. In our application, the latter provides the best results by preserving small meaningful objects such as poles and bollards while avoiding over-segmentation on more complex objects such as cars and trees.